To add onto what /u/spraak said, it's not just a Russian thing. English uses "the" as a way to indicate a region that is part of a larger whole. I'm not from th

To add onto what /u/spraak said, it's not just a Russian thing. English uses "the" as a way to indicate a region that is part of a larger whole. I'm not from the America, but I can be from the Midwest and enjoy hiking in the Catskills, and reminisce about that time I worked in the Bay Area. To refer to Ukraine as part of a larger whole, that larger whole is implied to be Russia.